This invention relates to a technology of erasing data stored in a storage system, and more particularly, to a technology of erasing a copy of data of an erasure target.
A storage area network (SAN) for connecting at least one external storage device with at least one computer has been known. The storage area network is especially useful when a plurality of computers share one large storage device. A storage system that includes such a storage area network has high extendibility because a storage device or a computer can be easily added thereto and eliminated therefrom.
For the external storage device connected to the SAN, a disk array device is generally used. The disk array device is a device on which many storage devices (such as magnetic disk drives) represented by hard disks are mounted.
The disk array device manages several magnetic disk drives as one group of redundant array of independent disks (RAID) by a RAID technology. The RAID group forms at least one logical storage area. The computer connected to the SAN executes a data I/O process in the storage area. The disk array device records redundant data in the magnetic disk drive of the RAID group when data is recorded in the storage area. Data can be restored from the redundant data even when one of the magnetic disk drives fails.
Additionally, a remote copy technology of copying data recorded in the disk array device to another disk array device has been known. By arranging a destination disk array device at a remote place, data loss damage caused by system failures, disasters, or the like can be suppressed.
A storage area of an erasure target is overwritten with dummy data to erase the data recorded in the magnetic disk drive. However, when the overwriting of dummy data is carried out only once, restoration of data may be allowed because of residual magnetism. Thus, a technology of completely erasing residual magnetism by repeating dummy data overwriting at least three or more times has been disclosed (refer to JP 2007-11522 A). Security risks can be reduced by completely erasing the residual magnetism to prevent data restoration.
A magnetic disk medium (hard disk drive) has widely been used for storing data. The data recorded in the magnetic disk medium has a characteristic in that it is restorable, because it is not completely erased through a simple file erasure operation or a volume formatting process. Especially because of magnetic disk characteristics, residual magnetism may remain on the medium, causing data restoration, when data overwriting is carried out only once, or after the formatting process.
A recent growing concern about security has been accompanied by a demand for a technology of completely erasing stored data. Therefore, a complete erasure process that repeats dummy data overwriting a plurality of times is useful for completely removing the residual magnetism from the magnetic disk.
On the other hand, even if the data stored in the storage device is completely erased, when backup data is stored, the data may leak from the backup data. Erasure of data may become difficult especially when management of backup data generated in the past is insufficient.
Moreover, in a case of creating a backup of the data of the magnetic disk drive in the magnetic disk drive, even when a source data area is overwritten a plurality of times to completely erase data, and replaced by zero data, overwriting is carried out only once in a destination data area if the zero data is only copied to a destination disk. As a result, residual magnetism remains, creating a possibility of data restoration.
In a remote copy environment, if the source storage area is overwritten a plurality of times to completely erase the data during data copy execution from the storage area of the source disk array device to the storage area of the destination disk array device, all the overwritten data are transferred to the destination disk array device. Thus, a great deal of traffic may adversely be generated in a remote copy network.